The use of diamond as an electronic material has remained elusive for many years. The problem lies in the difficulty of finding a way to dope diamond so that it""s ambient temperature conductivity and carrier mobility are sufficiently high to make diamond-based devices work at room or ambient temperature. Traditional doping with nitrogen does not work, since nitrogen forms a deep donor level 1.7 eV below the conduction band, and thus is not thermally activated at room temperature. This is due to the fact that nitrogen is very reluctant to insert into the diamond lattice, and all efforts to dope microcrystalline diamond with electrically active nitrogen have to date met with very limited success.
The inventors and others at Argonne National Laboratory have worked for several years developing the use of microwave plasma enhanced chemical vapor deposition (MPCVD) to produce ultrananocrystalline diamond (UNCD) thin films. These films are grown using argon-rich plasmas rather than the traditional hydrogen-rich plasmas, which are routinely used to grow microcrystalline diamond films, as disclosed in U.S. Pat. No. 5,462,776, the disclosure of which is incorporated by reference.
The UNCD films have grain boundaries are almost atomically abrupt (xe2x88x920.5 nm) and have been measured on the average of 0.3 to 0.4 nm. These UNCD films exhibit exceptional mechanical and tribological properties, the latter particularly applicable to the development of a new microelectromechanical system (MEMS) technology based on UNCD. For purposes of this application, UNCD shall be defined as films grown from C2 dimers, as set forth in the ""776 patent.
This invention relates to n-type doping of UNCD films, that is films with average grain size of less than about 15 nm, as opposed to films with larger grain sizes, such as microcrystalline or nanocrystalline diamond. When nitrogen gas was added to gas mixtures used to grow UNCD, the conductivity of the films unexpectedly increased by more than five orders of magnitude, while the grain boundaries and the grain size become larger.
Accordingly, it is an object of the present invention to provide an electrically conducting ultrananocrystalline diamond having about 1019 atoms/cm3 nitrogen with an electrical conductivity of not less than about 0.1 xcexa9xe2x88x921cmxe2x88x921.
Another object of the present invention is to provide an electrically conducting ultrananocrystalline diamond having an average grain size of about 15 nm or less and nitrogen present in an amount of not less than about 1019 atoms/cm3 made by the process of providing a source of carbon and a source of nitrogen and subjecting the sources of carbon and nitrogen in vapor form to an energy source in an noble-gas atmosphere to create a plasma to form an ultrananocrystalline material, wherein carbon is present in an amount less than about 2% by volume of the source gas.
Yet another object of the present invention is to provide a process for producing electrically conducting ultrananocrystalline diamond films, comprising subjecting a mixture of nitrogen and carbon containing gas and noble gas to an energy source to deposit nitrogen-incorporated ultrananocrystalline diamond films, wherein the atomic percent of carbon in the source gas is less that about 2%, and the nitrogen is present in the range of from about 2% to about 50% by volume to produce an ultrananocrystalline material with nitrogen present in an amount not less than about 1019 atoms/cm3.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.